The present invention relates to an information storage medium including a code storage portion, e.g., a bar code portion. The invention also relates to a method and an apparatus for judging if a subject information storage medium is real or not when the real medium is produced according to the present invention.
In recent years, code storage portions, for example, bar codes, which may be detected by optical readers, have been attached to various goods. Information recorded at such code storage portions may be utilized for merchandise management, e.g., distinction of items in POS (point of sale) system and so on. Usually, a bar code is constituted of black and white bars having different widths which cooperate to represent codes or information. An optical reader emits rays within a specific range of wavelength and receives the rays reflected from the bar code. Then, the reader can detect the widths of the black and white bars since the reflectance from the black bars and the reflectance from the white bars are remarkably different from each other.
However, such bar codes including black or dark bars may make the appearance of the goods cheap, so that it is not suitable to attach the visible bar codes to expensive, sophisticated or aesthetic goods. Therefore, bar codes, which do not absorb visible rays, but absorb infrared so as to be invisible for human beings, have been developed.
JP-A-57-201963 (published in 1982) and JP-A-1-305484 (published in 1989) discloses a bar code which is transparent for visible rays and absorbs infrared rays. However, conventional infrared absorbers absorb a wide range of wavelength. Thus, they are not transparent for visible rays completely in fact.
Accordingly, in order to conceal such bar codes, a cover layer, made of infrared-transparent and invisible materials, was proposed in JP-A-58-45999 (published in 1983).
Besides, JP-A-3-154187 (published in 1991) discloses that a cover layer, made of infrared-transparent and invisible materials made of materials, is mounted on a bar code made of an infrared absorber which absorbs infrared rays within the specific wavelength range between 700 nm and 1500 nm. These known techniques may resolve the above-described problem since the bar codes are difficult to be found by human beings and do not make the appearance of the goods cheap. On the other hand, it is a very important consideration that the code storage portions, e.g., bar codes or the like should be prevented from being forged or counterfeited. The above-described prior art techniques for concealing may be one of the means for protecting against forgers or counterfeiters since the bar codes are invisible. However, if a forger uses infrared scopes, the concealed bar codes can be inspected easily since the conventional infrared absorbers absorb a wide range of wavelength. In addition, since there are many kinds of infrared absorbers, it is not difficult to forge such bar codes using with known infrared absorbers on the basis of the inspection.
Accordingly, it is an object of the present invention to provide an information storage medium which is extremely difficult to be forged or counterfeited. Another object of the present invention is to provide a method and an apparatus for judging if a subject information storage medium is real or not when the real information storage medium is produced according to the present invention.
In accordance with the present invention, an information storage medium comprises a base portion and a code storage portion. The code storage portion is disposed on the base portion and contains a light absorber. The light absorber absorbs substantially only specific rays within a narrow wavelength band. It is preferable that the light absorber is an infrared absorber which absorbs substantially only infrared within a narrow wavelength band, but absorbs visible rays little.
With such a construction, since the infrared absorber absorbs substantially only infrared within a narrow wavelength band, the code storage portion is extremely difficult to be detected by means of infrared scopes in comparison with the conventional infrared absorbers which absorbs a wide range of wavelength of infrared rays. In addition, such an absorber absorbing substantially only specific rays within the narrow wavelength band is difficult extremely to be produced using with other components, and thus, it is prevented to forge or counterfeit the information storage medium according to the present invention. Besides, since the infrared absorber absorbs visible rays little, the code storage portion can be made invisible, and therefore may not make the appearance of expensive, sophisticated or aesthetic goods cheap.
In another aspect of the present invention, subject information storage mediums are judged real or not by a method in case that the real information storage medium includes a base portion and a code storage portion disposed on the base portion, the code storage portion containing a light absorber, the light absorber being capable of absorbing substantially only specific rays within a narrow wavelength band, the narrow wavelength band including a peak wavelength at which the light absorber absorbs the most. The method comprises the steps of emitting rays to the subject information storage medium, receiving rays reflected from the subject medium, detecting a first reflectance at the peak wavelength and a second reflectance at a comparison wavelength near the peak wavelength, and judging if the subject medium is real or not on the basis of the first reflectance and the second reflectance. The rays at the comparison wavelength are not absorbed by the light absorber very much. That is, the comparison wavelength is near or at the critical point of the narrow wavelength band which the light absorber absorbs.
By the method according to the present invention, since the comparison wavelength is near the peak absorption wavelength and the rays at the comparison wavelength are not absorbed substantially, an accurate detection of a forged medium is ensured. In other words, improved is the accuracy of judgement if an information storage medium is real or not.
Preferably, in the judging step, a difference between the first reflectance and second reflectance is obtained, and the subject medium is judged real if the difference between the first reflectance and the second reflectance is greater than a certain value. But, the subject medium is judged as a forgery if the difference is equal to or less than the certain value.
In this case, if the certain value is variable, it will be determined high for expensive goods which need high reliability. On the other hand, the certain value will be determined low for inexpensive goods which do not need high reliability.
The light absorber is preferably an infrared absorber being capable of absorbing substantially only infrared within a narrow wavelength band, but absorbing visible rays little, so that the code storage portion may be concealed. In this case, the rays used at the emitting step contain at least infrared rays which are absorbed by said light absorber.
It is preferable that the difference between the peak wavelength and the comparison wavelength is prescribed greater than 10 nm and equal to or less than 100 nm.
This means that the narrow wavelength band, which the light absorber absorbs, is very much narrow since the comparison wavelength is near or at the critical point of the narrow wavelength band as mentioned above. Such a light absorber may be made of only specific components practically, and thus subject information mediums will be judged as a forged one when the components are different from those of the real medium. Accordingly, the accuracy of the judgement is further improved.
In another aspect of the present invention, subject information storage mediums are judged real or not by an apparatus in case that the real information storage medium includes a base portion and a code storage portion disposed on the base portion, the code storage portion containing a light absorber, the light absorber being capable of absorbing substantially only specific rays within a narrow wavelength band, the narrow wavelength band including a peak wavelength at which the light absorber absorbs the most. The apparatus comprises an emitting means, receiving means and a judging means. The emitting means emits rays to the subject information storage medium, the rays containing at least rays of the peak wavelength and rays of a comparison wavelength near the peak wavelength, which are not absorbed by the light absorber very much. The receiving means receives the rays reflected from the subject medium and provides a first output signal in accordance with a first reflectance at the peak wavelength and a second output signal according to a second reflectance at the comparison wavelength. The judging means obtains the difference between the first signal and the second signal, and judges if the subject medium is real or not on the basis of the difference between the first signal and the second signal.
More preferably, the judging means judges the subject medium real if the difference between the first signal and the second signal is greater than a certain value, and judges the subject medium as a forgery if the difference is equal to or less than the certain value.
In a preferable aspect, the emitting means emits at least infrared rays for inspecting the subject medium when the light absorber of the real information storage medium is an infrared absorber, the infrared absorber being capable of absorbing substantially only infrared within a narrow wavelength band, but absorbing visible rays little.
It is also preferable that a difference between the peak wavelength and the comparison wavelength, by which the receiving means provides the first and second output signals, is prescribed greater than 10 nm and equal to or less than 100 nm.